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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1962

Pitfalls in thermal emission studies

Attention is called to several pitfalls that often beset investigators who make thermal emittance studies. The pitfalls mentioned include the following: (1) conflicting meanings of several frequently used terms as found in the literature, each meaning having authoritative sponsorship; (2) incomplete and hence potentially misleading descriptions of specimens on which reported data arc based; (3) reference to emissivity or remittance as a property of a surface rather than a volume property (influenced by the surface); (4) occasional omission of diffuse reflection from analyses of the optical properties of inhomogeneous bodies; (5) failure to observe the restrictions upon conditions that are required for validity of basic equations; (6)uncertainties as to the effective temperature, peculiar to specimens having low absorption indices; and (7) lack of suitable physical standards. Several suggestions are made for avoid­ing or minimizing the consequences of the pitfalls discussed.

THERMAL RADIATION↗
NASA NTRS1986

Common problems and pitfalls in gear design

There are several pitfalls and problems associated with the successful design of a new gear transmission. A new design will require the knowledge and experience of several technical areas of engineering. Most of the pitfalls and problems associated with a new design are related to an inadequate evaluation of several areas, such as, the lubrication and cooling requirements, complete static and dynamic load analysis, evaluation of materials and heat treatment and the latest manufacturing technology. Some of the common problems of the gear design process are discussed with recommendations made for avoiding these conditions.

Townsend, Dennis P.↗
NASA NTRS2000

Potential Pitfalls Related to Space-Based Lidar Remote Sensing of the Earth with an Emphasis on Wind Measurement

A collection of issues is discussed that are potential pitfalls, if handled incorrectly, for earth-orbiting lidar remote sensing instruments. These issues arise due to the long target ranges, high lidar-to-target relative velocities, low signal levels, use of laser scanners, and other unique aspects of using lasers in earth orbit. Consequences of misunderstanding these topics range from minor inconvenience to improper calibration to total failure. We will focus on wind measurement using coherent detection Doppler lidar, but many of the potential pitfalls apply also to noncoherent lidar wind measurement, and to measurement of parameters other than wind. Each area will be identified as to its applicability.

Kavaya, Michael J.↗
NASA NTRS2000

Potential Pitfalls Related to Space-Based Lidar Remote Sensing of the Earth With an Emphasis on Wind Measurement

A collection of issues is discussed that are potential pitfalls, if handled incorrectly, for earth-orbiting lidar remote sensing instruments. These issues arise due to the long target ranges, high lidar-to-target relative velocities, low signal levels, use of laser scanners, and other unique aspects of using lasers in earth orbit. Consequences of misunderstanding these topics range from minor inconvenience to improper calibration to total failure. We will focus on wind measurement using coherent detection Doppler lidar, but many of the potential pitfalls apply also to noncoherent lidar wind measurement, and to measurement of parameters other than wind.

Kavaya, Michael J.↗
NASA NTRS1984

Avoiding pitfalls in simulating real-time computer systems

The software simulation of a computer target system on a computer host system, known as an interpretive computer simulator (ICS), functionally models and implements the action of the target hardware. For an ICS to function as efficiently as possible and to avoid certain pitfalls in designing an ICS, it is important that the details of the hardware architectural design of both the target and the host computers be known. This paper discusses both host selection considerations and ICS design features that, without proper consideration, could make the resulting ICS too slow to use or too costly to maintain and expand.

Smith, R. S.↗
NASA NTRS1985

EL2 and related defects in GaAs - Challenges and pitfalls

The incorporation process of nonequilibrium vacancies in melt-grown GaAs is strongly complicated by deviations from stoichiometry and the presence of two sublattices. Many of the microdefects originating in these vacancies and their interactions introduce energy levels (shallow and deep) within the energy gap. The direct identification of the chemical or structural signature of these defects and its direct correlation to their electronic behavior is not generally possible. It is necessary, therefore, to rely on indirect methods and phenomenological models and deal with the associated pitfalls. EL2, a microdefect introducing a deep donor level, has been in the limelight in recent years because it is believed to be responsible for the semi-insulating behavior of undoped GaAs. Although much progress has been made towards understanding its origin and nature, some relevant questions remain unanswered. An attempt is made to assess the present status of understanding of EL2 in the light of most recent results.

Gatos, H. C.↗
NASA NTRS1985

EL2 and related defects in GaAs - Challenges and pitfalls

The incorporation process of nonequilibrium vacancies in melt-grown GaAs is strongly complicated by deviations from stoichiometry, and the presence of two sublattices. Many of the microdefects originating in these vacancies and their interactions introduce energy levels (shallow and deep) within the energy gap. The direct identification of the chemical or structural signature of these defects and its direct correlation to their electronic behavior is not generally possible. It is therefore necessary to rely on indirect methods and phenomenological models and be confronted with the associated pitfalls. EL2, a microdefect introducing a deep donor level, has been in the limelight in recent years because it is believed to be responsible for the semi-insulating behavior of undoped GaAs. Although much progress has been made towards understanding its origin and nature, some relevant questions remain unanswered. An attempt is made to assess the present status of understanding of EL2 in the light of the most recent results.

Gatos, H. C.↗
NASA NTRS1990

Pitfalls

Though potentially of great benefit to the nation, the experience of the workshop participants and their discussions with Sea Grant and Land Grant officials make it clear that the Space Grant Program must avoid certain pitfalls of the past and present if it is to be successful. The most important of these are listed and briefly discussed.

Triffet, Terry↗
NASA NTRS2000

Potential pitfalls of strain rate imaging: angle dependency

Strain Rate Imaging (SRI) is a new echocardiographic technique that allows for the real-time determination of myocardial SR, which may be used for the early and accurate detection of coronary artery disease. We sought to study whether SR is affected by scan line alignment in a computer simulation and an in vivo experiment. Through the computer simulation and the in vivo experiment we generated and validated safe scanning sectors within the ultrasound scan sector and showed that while SRI will be an extremely valuable tool in detecting coronary artery disease there are potential pitfalls for the unwary clinician. Only after accounting for these affects due to angle dependency, can clinicians utilize SRI's potential as a valuable tool in detecting coronary artery disease.

NASA Discipline Cardiopulmonary↗
NASA NTRS2016

Pitfalls and Precautions When Using Predicted Failure Data for Quantitative Analysis of Safety Risk for Human Rated Launch Vehicles

Launch vehicle reliability analysis is largely dependent upon using predicted failure rates from data sources such as MIL-HDBK-217F. Reliability prediction methodologies based on component data do not take into account risks attributable to manufacturing, assembly, and process controls. These sources often dominate component level reliability or risk of failure probability. While consequences of failure is often understood in assessing risk, using predicted values in a risk model to estimate the probability of occurrence will likely underestimate the risk. Managers and decision makers often use the probability of occurrence in determining whether to accept the risk or require a design modification. Due to the absence of system level test and operational data inherent in aerospace applications, the actual risk threshold for acceptance may not be appropriately characterized for decision making purposes. This paper will establish a method and approach to identify the pitfalls and precautions of accepting risk based solely upon predicted failure data. This approach will provide a set of guidelines that may be useful to arrive at a more realistic quantification of risk prior to acceptance by a program.

Hatfield, Glen S.↗
NASA NTRS2016

Pitfalls and Precautions When Using Predicted Failure Data for Quantitative Analysis of Safety Risk for Human Rated Launch Vehicles

Launch vehicle reliability analysis is largely dependent upon using predicted failure rates from data sources such as MIL-HDBK-217F. Reliability prediction methodologies based on component data do not take into account system integration risks such as those attributable to manufacturing and assembly. These sources often dominate component level risk. While consequence of failure is often understood, using predicted values in a risk model to estimate the probability of occurrence may underestimate the actual risk. Managers and decision makers use the probability of occurrence to influence the determination whether to accept the risk or require a design modification. The actual risk threshold for acceptance may not be fully understood due to the absence of system level test data or operational data. This paper will establish a method and approach to identify the pitfalls and precautions of accepting risk based solely upon predicted failure data. This approach will provide a set of guidelines that may be useful to arrive at a more realistic quantification of risk prior to acceptance by a program.

Hatfield, Glen S.↗
NASA NTRS1971

Some Pitfalls of Urine Analysis

Possible failures or erroneous findings during routine urine analysis are surveyed. Data cover tablet, tape, and stick type analysis techniques.

Townsend, F. M.↗
NASA NTRS1979

Space platforms for NASA - Opportunity or pitfall

The paper describes NASA efforts to determine if platform to pool payload services are cost effective. It is shown that the platform concept originated from the short Shuttle life on orbit, the Shuttle capability to assemble aggregating structures, and the belief that economics might be obtained from shared services and repair. In addition, about eighty payloads in NASAs future were identified for consideration. Attention is given to platform configurations produced by contractor and in house studies, noting that comparative cost studies are currently being done.

Cuneo, W. J., Jr.↗
NASA NTRS1981

Pitfalls and guidelines for the numerical evaluation of moderate-order system frequency response

The design and evaluation of a feedback control system via frequency response methods relies heavily upon numerical methods. In application, one can usually develop low order simulation models which for the most part are devoid of numerical problems. However, when complex feedback interactions, for example, between instrument control systems and their flexible mounting structure, must be evaluated, simulation models become moderate to large order and numerical problems become common. A large body of relevant numerical error analysis literature is summarized in a large language understandable to nonspecialists. The intent is to provide engineers using simulation models with an engineering feel for potential numerical problems without getting intertwined in the complexities of the associated mathematical theory. Guidelines are also provided by suggesting alternate state of the art methods which have good numerical evaluation characteristics.

Frisch, H. P.↗
NASA NTRS1982

Some solutions to the problems and pitfalls of laser velocimetry in a large transonic wind tunnel

Attention is given to engineering design and development features of a two-component, coaxial backscatter laser velocimetry system which attempts to realize the long-recognized desirability of this technique's use for nonintrusive flow measurement. The design of the optics for the present 16-foot transonic wind tunnel device, and problems associated with the installation of the system in the hostile, test section plenum chamber environment are discussed.

Reubush, D. E.↗
NASA NTRS1986

Operational wave forecasting with spaceborne SAR: Prospects and pitfalls

Measurements collected in the Shuttle Imaging Radar (SIR-B) Extreme Waves Experiment confirm the ability of Synthetic Aperture Radar (SAR) to yield useful estimates of wave directional energy spectra over global scales, at least for shuttle altitudes. However, azimuth fall-off effects tend to become severe for wavelengths shorter than about 100 m in most sea states. Moreover, the azimuth fall-off problem becomes increasingly severe as the platform altitude increases beyond 300 km. The most viable solution to the global wave measurements problem may be a low altitude spacecraft containing a combination of both the SAR and the Radar Ocean Wave Spectrometry (ROWS). Such a combination could have a synergy which yield global spectral estimates superior to those of either instrument singly employed.

Beal, R. C.↗